Yes, all babies have a power to scream so loud to make Superman bleed out of his ears.
Its very common.
That is why we generally keep babies in a series of soundproof rooms under a mountain until they lose their abilities.

Not necessarily;
Injustice is merely a seperate universe to convey a set list of ideas and "What Ifs" for certain characters, the main one being what if Superman was more intervening with his powers, but side ones including what if things had gotten more serious with Joker and Harley.

I think in general, it can be assumed Harley and Joker boned, cause I mean, c'mon
But I don't think it's ever been canon they boned to the point of a child being born from it.

The entire Arkham game line is an alternate, elseworld universe though just like Injustice, which would still render any occurences to the characters, including Joker's death

Also, it should be noted that Harley Quinn has several pregnancy tests that went up negative (as shown in the Manager's Office a la Harley Quinn's Revenge DLC), with the box even stating on the inside that there's a chance of a false positive. So it's quite likely even in the Arkham elseworld there's no pregnant Harley Quinn either.
(Sefton Hill, founder of Rocksteady whom developed the Arkham games, confirmed for himself that it was a false positive as well, as reported on the wiki) batman.wikia.com/wiki/Harley_Quinn_(Batman:ArkhamCity)#Trivia

But the again, so are all the comics in a way. There's no absolute "canon" batman storyline for instance. They're just different iterations and versions of an established character. So one batman is different from another in a way. The storylines are all big "what ifs."

The way you always use exclamation points makes me think of you speaking with an unnatural amount of happy in your voice
Like you could make "I just killed you parents!" sound so happy Batman wouldn't be mad at you.

Superman's sanity was breaking, and he found Green Arrow in the Fortress of solitude, where his parents were being kept for their safety. After a few major power-plays by supes, the US government attempted to take his family, to show him not to mess with them. It didn't work out. So Supes got... A bit carried away, thinking he was there to take them again. He was only there on Batman's orders, to get the Super Pill (Which he still got to Black Canary, despite his death).

In my english class a friend and i were talking about batman cause she loves him and I said how much I like Harley Quinn. My english teacher walked past and said "thats an unhealthy waifu" I nearly **** myself
Serious though, I ******* love Harley Quinn